Catheter system

ABSTRACT

A cryocatheter for treatment of tissue has a tip adapted to provide a signal indicative of the quality and/or orientation of the tip contact with surrounding tissue. In one embodiment, a signal conductor extends through the catheter to the tip and connects to a thermally and electrically conductive shell or cap that applies an RF current to the region of tissue contacted by the tip. The tissue impedance path between the signal lead and a surface electrode mounted on the patient&#39;s skin is monitored to develop a quantitative measure of tissue contact at the distal tip, which is preferably displayed on the screen of a catheter monitoring console. In yet a further embodiment, the catheter is provided with a split tip having temperature monitoring sensors, such as thermistors, mounted on opposed halves of the tip so as to sense temperature on two sides of the catheter axis. The thermistor signals are processed to determine and display differential temperature between the two sides of the tip, thus revealing which side lies in contact. In yet a further aspect of the first embodiment, two separate and distinct high frequency electrical signals are applied to the two halves of a split metal shell or cap at the tip. Signals received at the surface electrode are filtered into first and second frequency components, and these are processed to determine the relative magnitude of the signal or the impedance of the path for each of the injected signals to determine and display the tissue contact orientation of the catheter. The catheter preferably has two separate cooling chambers within the cooling tip, positioned with one chamber on each side of the axis, and a separate cooling inlet to each chamber is switched on by a valve which directs the flow of coolant to the contact side during active cryotreatment. In another embodiment, the cap provides an RF electrode that may be opposed to the cooling side so that either the cryogenic or the RF ablation side may be rotated into contact to selectively heat or cool, or in representative protocol treat, then thaw, the same tissue site.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.09/393,461, filed Sep. 10, 1999, now U.S. Pat. No. 6,471,693.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

Not Applicable.

FIELD OF THE INVENTION

The present application relates to cryocatheters and wands, i.e. tocatheters and wands which are used to treat tissue by cooling contact.Such implements, henceforth generically referred to herein as“cryocatheters” or simply “catheters” have an elongated body throughwhich a cooling fluid circulates to a tip portion which is adapted tocontact and cool tissue. In general, cryocatheters may be used to lowerthe temperature of tissue, such as cardiac wall tissue, to an extentsuch that signal generation or conduction ceases and allows one to mapor confirm that the catheter is positioned at a particular lesion orarrhythmia conduction site. They may also be configured for ablationtreatment, to cool the tissue to a much lower level at which freezingdestroys the viability of the tissue, and, in the case of cardiactissue, permanently removes it as a signal generating or signalconducting locus. Such devices are also useful for destruction of tissueat other body sites, such as the ablation of tumorous, diseased,precancerous or congenitally abnormal tissue in various vessel or organsystems.

Cryocatheters may be adapted for endovascular insertion, or forinsertion along relatively confined pathways, for example through a bodylumen, or through a small incision to and around intervening organs, toreach an intended ablation site. As such, they are characterized by anelongated body through which the cooling fluid must circulate, and a tipor distal end portion where the cooling is to be applied. Therequirement that the coolant be localized in its activity posesconstraints on a working device. For example when the catheter contactmust chill tissue to below freezing, the coolant itself must attain asubstantially lower temperature. Furthermore the rate of cooling islimited by the ability to supply coolant to and circulate it through theactive contact region, and the efficacy of the contact region itself isfurther limited by geometry and physical properties that affect itsability to conduct heat into the tissue. The achievable rate of coolingmay be impaired by warming due to residual circulation, and it alsochanges depending upon the effectiveness of thermal contact, e.g. uponthe contact area and contact pressure between the catheter and thetissue, as well as being influenced by ice accumulations or otherartifacts or changes due to the freezing process itself. Moreover, it isa matter of some concern that proximal, adjacent or unintended tissuesites should not be exposed to harmful cryogenic conditions. Thesesomewhat conflicting requirements make the implementation of aneffective cryocatheter a complex matter.

One approach has been to provide a phase change coolant which is pumpedas a liquid to the tip of the catheter and undergoes its phase change ina small chamber located at the tip. The wall of the chamber contactsadjacent tissue directly to effect the cooling or ablation treatment.Such a device can treat or achieve a relatively high rate of heat energytransfer. Moreover, by employing a phase change refrigerant which may beinjected at ambient temperature along the body of the catheter andundergo expansion at the tip, the cooling effect may be restricted tothe localized treatment region surrounding the tip portion of thedevice. The dimensions of catheter construction, particularly for anendovascular catheter, require that the phase change coolant be releasedfrom a nozzle or tube opening at a relatively high pressure, into arelatively small distal chamber of the catheter. After the fluid expandsin the distal chamber and cools the walls, it is returned through thebody of the catheter to a coolant collection system, preferably in theform of a recirculation loop.

Catheters or treatment wands of this type for endovascular or endoscopicuse generally have a relatively symmetrical profile such as apencil-like cylindrical shape or a bullet-like shape, and they mayinclude various steering mechanisms for curving the tip to urge itagainst the tissue which is to be treated. Fluoroscopic visualizationmay be used both for positioning the catheter tip initially and forobserving the progress of ice formation. However, the cooling effect isextremely local, relying on thermal conduction through contact, and themethod of visualization may involve a plane projection, or may otherwiselack precision or resolution. Also, because of the extreme temperaturesinvolved, the tip of the catheter may freeze to tissue which itcontacts, preventing any further adjustment or repositioning of the tiponce cooling has started. Moreover, if the catheter constructioninvolves any degree of asymmetry, the fluoroscopic representation may beinsufficient to determine the effective area of contact or expectedcooling profile in surrounding tissue.

It has been proposed, for example in U.S. Pat. No. 5,667,505, thatbecause of the impossibility of measuring the tip-to-tissue contact, oneinstead measure the temperature of a heat exchanger, and utilize astandard heat capacity measurement to develop appropriate controlsignals. Furthermore, with these and other types of ablation catheters,various detection systems have been proposed for determining the degreeof contact or the extent of heating. See, for example, U.S. Pat. Nos.5,743,903, 5,810,802, 5,759,182 and 5,643,255. However, to the best ofapplicant's knowledge, such devices do not address the need for a simplepositioning system for a cryogenic treatment catheter.

Accordingly, there remains a need for a cryocatheter tip constructionthat effectively determines, reports or controls tissue contact.

There is also a need for a cryocatheter construction that moreeffectively cools contacted tissue.

There is further a need for a cryocatheter positioning system which iscontrollable to apply cooling to a predetermined tissue region.

SUMMARY OF THE INVENTION

One or more of the foregoing desirable objects are achieved inaccordance with embodiments of the present invention by a cryocatheterfor treatment of tissue wherein the tip of the catheter is adapted toprovide a signal indicative of the quality and/or orientation of the tipcontact with surrounding tissue. In one embodiment, a signal conductorextends through the catheter to the tip and connects to a thermally andelectrically conductive shell or cap to apply a high frequencyelectrical signal to the region of tissue contacted by the tip. Asurface electrode is mounted on the patient's skin, and the tissueimpedance path between the signal lead and the surface electrode ismonitored to develop a quantitative measure of tissue contact in thecooling region of the distal tip. Preferably this measure is displayedon the screen of a catheter monitoring console. In yet a furtherembodiment, the outer portion of the tip is provided with a splitthermally conductive jacket, and temperature monitoring sensors, such asthermistors or thermocouples, are mounted on both halves of the tip soas to sense temperature separately on two opposite sides of the catheteraxis. The thermal signals are processed to indicate and display thedifferential temperature between the two sides of the tip, thusproviding an indication of which side lies in contact with tissue.

In yet another aspect of the first embodiment utilizing a splitconductive shell or cap, two separate and distinct high frequencyelectrical signals are applied to the two halves of the split tip. Inthat case, the signal received at the surface electrode is filtered intofirst and second frequency components, and these are processed todetermine the relative strength of each signal component to provide anindication of the relative impedance of the path for each signal, andthus the console determines and displays the tissue contact orientationof the catheter tip itself. The system of this embodiment preferablyutilizes a catheter which has separate cooling or refrigerant expansionor circulation chambers within the cooling tip. These may be positionedso that one chamber lies on each side of the axis at the tip region, andeach is associated with its own thermistor or other sensor, and its ownconductive wall portion. A controller monitors the temperature sensor orRF conduction of the signal electrode associated with each chamber, andthe control console display indicates the tissue-contacting side of thecatheter. This cryocatheter preferably includes a separate cooling inletto each chamber, and a mechanism in or connected to the handle fordirecting the flow of coolant to one or the other chamber during activecryotreatment. The console may further include a controller toautomatically control the valve to direct coolant to thetissue-contacting side.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be more fully understood from the detailed discussionbelow of several examples taken in conjunction with drawings ofillustrative embodiments, in which:

FIG. 1 shows a cryoablation catheter and system of the presentinvention;

FIG. 2 illustrates a first embodiment of a catheter of the invention;

FIG. 3 illustrates a second embodiment of a catheter of the invention;

FIG. 4 shows a third embodiment of a catheter of the invention; and

FIGS. 4A and 4B show further embodiments with alternative coolingarrangements.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a cryogenic treatment system 100 illustratingrepresentative elements thereof. System 100 includes a treatmentcatheter 110 having a handle 110 a, and elongated cryogen transportingbody 110 b and a catheter tip 110 c. The catheter 110 is connected byvarious conduits or cables 115 to a console 120 which may, for example,perform control and monitoring functions, and may have a display monitor120 a and other data entry or display accessories such as a keyboard, aprinter and the like. The lines 115 may include a coolant injection line115 a, a coolant return line 115 b, and electrical cabling 115 c whichmay carry outputs of various cardiac sensing, thermal sensing, mappingor other elements such as are commonly used for catheter treatment ormonitoring. As shown, the handle 110 a is equipped with input ports foran electrical connector 111, a coolant injection tube connector 112, anda return tube connector 113. These connect by various internal junctionsor tubes passing through the handle and elongated body 110 b to thedistal tip of the catheter. The handle may also include deflectionmechanisms, various control assemblies, e.g., switches or valves, aswell as safety detection or shutdown elements (not illustrated), some ofwhich are discussed further below.

As shown schematically in FIG. 2, the coolant is carried to the tipthrough a tube 1 and enters a chamber 3 at the end of the catheter tip110 c via a nozzle 2 at the end of the tube to expand in a smallcontained region forming the active cooling region of the tip of thecatheter. By way of example, the tube 1 may run centrally within theelongated body 110 b, and the portion of the body lumen outside of tube1 may form a return passage for spent coolant. After coolant exits froman orifice 2 at the end of the tube, it returns through the space 6surrounding the tube 1 to the fluid return connector 113 of the handle(FIG. 1). The return passage for expended coolant may be a vacuumpassage, thus assuring that leakage out of the catheter into thebloodstream does not occur, and providing some additional thermalinsulation of the fluid line running along its interior.

In the illustrated embodiment, the chamber 3 in which coolant isreleased from the nozzle 2 and whence it returns to the return passagevia opening 4, defines the cooling region of the catheter tip. Thischamber may be short, less than a few centimeters long, and located atthe very tip of the catheter or slightly proximal thereto. The activecooling chamber has a thermally conductive wall 7 for efficientlyconducting heat from the adjacent tissue, and for the illustratedendovascular embodiment this takes the form of a metal cap that mayadvantageously be steered into contact with the tissue by a simplebending deflection of the tip region. In accordance with a principalaspect of the present invention, the chamber is also equipped withelements for sensing which portion of the tip has been brought intocontact with tissue. In the illustrated embodiment, this is achievedusing first and second thermocouples 5 a, 5 b positioned on oppositesides of the chamber 3. In the case of a cardiac catheter, one or morering electrodes 8 a, 8 b, 8 c (FIG. 1) may be positioned at the cathetertip for performing signal sensing and/or position monitoring functions.

While the foregoing description describes a cryogenic catheter system ingeneral terms with several elements which are or may be useful in such asystem, applicant specifically contemplates as a preferred embodiment acryoablation system that utilizes a phase change coolant injectedthrough the coolant line 1 to expand in the chamber 3 at the tip of thecatheter, and return via a vacuum or suction passage to the returnconnection 113 at the catheter handle. In a system of this typedeveloped by the assignee of the present invention, the phase changematerial is provided at ambient temperature but relatively high pressurethrough the handle and body 110 a, 110 b of the catheter, such thatcooling only occurs upon release of pressure and expansion within thechamber 3 at the tip of the catheter. Operation of this device involvescontrolling the timing and amount of coolant injected through the inlettube 1, and/or the injection pressure, which may, for example, be apressure up to about 500 psig. The entire catheter with such a localizedcooling mechanism may be dimensioned to fit in a No. 9 French introduceror smaller. Similar coolant systems may be incorporated in hand-heldcryotreatment or ablation units for endoscopic application.

In accordance with the principal aspect of the present invention, thesensor signals, for example from the thermocouples 5 a, 5 b are providedto the monitor and control console 120 which may in addition receiveother system inputs from sensors related to the cooling system, cardiacsensing electrodes or positioning or mapping elements of the cathetersystem. As shown, the controller 120 communicates with or includes aprocessor 122 and the display 120 a, and it may operate in a mannerknown in the art to perform such display functions as for exampleoverlaying a radiographic image of the catheter and patient with varioussynthetically created images, for example, representing mapping pointsor thermal or physiological data derived from sensor measurements. Thecontroller 120 may also produce output signals, for example to controlthe flow of coolant in response to detected trigger signals, temperaturestates or other conditions in an automated program or manuallycontrolled manner.

In an exemplary mode of operation for a system having opposedthermocouples 5 a, 5 b as shown in FIGS. 1 and 2, the processor 122 maysimply detect the outputs of both thermistors and determine thedifference in temperature between the two sensing positions. In thatcase, the colder sensor may correspond to the sensor on the side thatdirectly contacts tissue (it being assumed, in the case of anendovascular or cardiac system, that blood flow has a warming effect onthe cryocatheter).

FIG. 3 shows another embodiment of a catheter system of the presentinvention. As shown in FIG. 3, the tip portion or tissue-contactingportion, when the chamber is located slightly proximal of the tip, isformed with a themally conductive outer shell or cap 15 which, asillustrated, is split into two halves 15 a, 15 b such that one half 15 acovers one side of the catheter and another half 15 b lies opposite,across the midplane or axis of the catheter. This split shellconstruction may be used with the catheter of FIGS. 1 and 2, in whichcase each of the thermocouples 5 a, 5 b is preferably mounted in contactwith or in a slight recess at the surface of, a corresponding one of thehalf shells 15 a, 15 b. In that case the cap serves not only to enhanceheat conduction through the chamber wall, but also to spread oruniformize the level of heat present generally at the side on which itis mounted. The thermally conductive halves 15 a, 15 b may extend forslightly different lengths along the axial direction of the catheter,making their positions and thus the catheter orientation visibleradiographically, due to possible radiographic opacity of theirstructure and their distinct visual appearance on the display.

In accordance with another aspect of the invention, rather thanemploying thermal sensing elements 5 a, 5 b, the positioning system ofthe present invention may operate by means of impedance sensing todetect tissue contact or catheter orientation. In accordance with thisaspect of the invention a body electrode is provided, such as a largearea surface electrode, and the impedance path between each of theconductive shell pieces 15 a, 15 b and the body electrode is monitored.This may be done by applying a high frequency or alternating signal tothe surface electrode and detecting the signal at a catheter leadextending from each of the separate shells 15 a, 15 b. This signal shallhereinafter be simply referred to as an “RF signal” although the termRF, as used in different technical fields and various countries istechnically more restrictive than the intended class of alternatingsignal energy. The strength of the signal so detected provides anindication of impedance path between the respective catheter electrodeson the two sides of the cooling segment, and the surface electrode.Since the major portion of the tissue pathway is identical for bothsides of the catheter, the detected impedance of the two halves willdiffer largely as a function of the local tissue contact at the coolingtip. Thus, it suffices to find the electrode having the lowestimpedance, or to derive a measure, such as the ratio of the two signals,that may be used as a binary (GO/NO GO) indicator of which side is incontact. Thus, for example if the ratio of the signal strength atelectrode 15 a to that of electrode 15 b is taken as the detectionthreshold, a ratio greater than one indicates that electrode 15 a makesbetter electrical contact and a ratio less than one indicates thatelectrode 15 b makes the better contact. As may be surmised from thediscussion of the temperature differential, above, the foregoing rulewould apply in circumstances where the catheter is used in a blood-freeenvironment. When the catheter resides in a full vessel, then contact bythe saline blood solution may provide a better electrical pathway. Thisresults in the opposite detection algorithm, i.e., the low-impedancepath is through the non-tissue-contacting side of the catheter.

As a variation on this detection method, the RF signals may be providedto the two separate shell portions 15 a, 15 b of the catheter of FIG. 3,and detected at the surface electrode. In this case, preferably signalsof two different frequencies f₁, f₂ are provided at the catheter tip tothe two electrically-separated electrode halves. The processor 122 ofthe controller 120 may then synchronously demodulate the detectedsignals arriving from the respective electrodes at the surfaceelectrode, at their respective frequencies, cumulating and determiningthe strength of the signal over some time interval before taking a ratioof the detected signals. Again the relative impedance of the twopathways identifies which electrode has made contact with tissue.

In accordance with a preferred aspect of the positioning system of thepresent invention, the cryocatheter has a cooling region comprised oftwo separate compartments 3 a, 3 b forming a split chamber as shown inFIG. 4. In this embodiment, coolant may be directed into either thefirst chamber 3 a or a second chamber 3 b lying on opposite sides of thecatheter axis by corresponding fluid inlets 2 a, 2 b, respectively,attached to the fluid source. This may be done by providing a switchedvalve SF operably connecting either of the inlets. Alternatively, twoseparate supply lines 1 a, 1 b switched at the control console 120 or inthe catheter handle may be employed, as indicated in FIG. 4A. Switchedcooling may also be accomplished by providing a single coolant line 1which is physically moved or steered by a steering wire 1 c to directits coolant into one or the other chamber as shown in FIG. 4B. Each ofthe chambers 3 a, 3 b is associated with one of the surface electrodesor conductive shell portions 15 a 15 b (FIG. 3), or thermal sensors(FIG. 2), and for example each of the half-jackets or electrodes 15 a,15 b may form a wall of one of the chambers. When employed withtemperature sensors such as thermistors, each chamber has a sensormounted on its contact wall.

Operation of this split chamber or bifurcated embodiment proceeds asfollows. The controller is configured to carry out a monitoring or aninitial procedure wherein it detects the side of the catheter in contactwith tissue. Then for cooling operation, the controller controls a valvewhich may for example be located in the handle of the catheter assemblyso as to preferentially cool one of the chambers 3 a or 3 b which it hasdetermined to reside in contact with the tissue. This allows the coolantto be more effectively used to cool the tissue side of the catheter.When the tissue contact detection mechanism is that of electrodes and RFsignal impedance, the controller simply actuates a valve to directcoolant to the detected contacting side of the catheter. Preferably, thecoolant may also be manually switched at the handle from one side to theother.

When the thermistor assembly as shown in FIG. 1 is employed as thecontact detection mechanism, the controller preferably initiates asomewhat more complex initial procedure whereby each chamber 3 a and 3 bis cooled, simultaneously or successively, at a low level of coolingwhile the temperature response is measured. The processor thendetermines from the response which side is cooling more quickly orotherwise exhibits a thermal characteristic such that it is deemed to bein contact with body tissue. Based on this determination, the controllerthereafter controls the cryogenic cooling regimen to preferentially coolthat side of the catheter tip. Thus, the present invention contemplatesa catheter wherein both the catheter cooling region and the catheterarrangement of sensors may discriminate between two sides, so as todetect the contacting side and then to more effectively cool the portionof the catheter that has contacted tissue.

The invention further contemplates that in embodiments wherein thetissue impedance is determined via signals conducted through aconductive cap or shell, this impedance may be detected by attaching thecatheter to a conventional RF ablation catheter, console, in which, forexample, such impedance measurements are customarily performed toprovide a control input for monitoring the degree of ablation and forthe RF ablation power control. In that case, the catheter of the presentinvention may also operate as an RF ablation electrode with the metalcap 7, 15 driven by the RF catheter console. The conductive cap or shellmay be split, and different regions of the cap may be connected to abipolar RF driver so that ablation energy warms or ablates tissue at agap between the bipolar electrodes. In this case, the electrode gap maybe positioned so that the heating region is angularly offset around thecatheter tip from the cooling wall of the cooling chamber. This allowsthe catheter to treat an identified site either by RF heating or bythermally conductive cooling, by simply rotating the catheter toposition the cooling wall or the electrode gap at the intended site.

The invention being thus disclosed and several operative embodimentsdiscussed, various additional constructions adapting the invention toknown catheters and control systems, and other variations andmodifications of the disclosed invention, will occur to those skilled inthe art, and it will be understood that such adaptations, variations andmodifications are all within the spirit and scope of the invention.Accordingly, the invention is not limited to the described embodiments,but encompasses all subject matter defined by or falling within thescope of the claims appended hereto and equivalents thereof.

What is claimed is:
 1. A catheter system comprising: an elongated body;a first tissue treatment unit for cooling tissue, having a tissuecooling portion disposed on said elongated body, the cooling portionhaving a thermally and electrically conductive outer shell defining aninterior through which cooling fluid passes to cool the outer shell; asecond tissue treatment unit for heating tissue, having a tissue heatingtreatment portion disposed on the elongated body, and having at leastone electrode for carrying an RF signal for tissue heating, the at leastone electrode being coupled with the electrically conductive outershell; and a control console for controlling tissue treatment, thecontrol console being operable to control the first and second tissuetreatment units, the control console being coupled to the at least oneelectrode to provide an RF signal to flow through the at least oneelectrode, and the control console being operable to measure animpedance input relative to a tissue pathway in communication with saidat least one electrode and operable to adjust tissue heating in responseto said impedance input, wherein the at least one electrode includes afirst electrode and a second electrode, the electrically conductiveouter shell defining an electrode gap having a first boundary and asecond boundary, the first boundary being disposed adjacent to the firstelectrode, the second boundary being disposed adjacent to the secondelectrode.
 2. The catheter system of claim 1, wherein the controlconsole measures a differential impedance between the first and secondelectrodes.
 3. The catheter system of claim 1, wherein the controlconsole includes an RF driver to control tissue heating proximate theelectrode gap.
 4. A catheter system comprising: an elongated body havinga tissue treatment portion, the tissue treatment portion including aconductive outer shell having an expansion chamber through which a flowof cooling fluid passes to cool the outer shell, and at least oneelectrode incorporated in said outer shell for carrying a flow of an RFsignal for tissue heating; wherein the at least one electrode includes afirst electrode and a second electrode, the conductive outer shelldefining an electrode gap having a first boundary and a second boundary,the first boundary being disposed adjacent to the first electrode, thesecond boundary being disposed adjacent to the second electrode; andfurther comprising a control console for controlling tissue treatment,the control console being operable to control the flow of cooling fluidand the flow of RF signal, wherein the control console is operable tocool the outer shell simultaneously with the flow of RF signal and tocool the outer shell in response to heating of the shell caused by theflow of RF signal to said shell, the control console measuring adifferential impedance between the first and second electrodes, andincluding an RF driver to control tissue heating proximate the electrodegap.
 5. The catheter system of claim 4, wherein the control console isoperable to heat a region proximate and angularly offset around theconductive outer shell.
 6. A method of treating tissue, including thesteps of: providing a catheter having a cryogenic fluid cooling elementand an RF tissue heating element, cooling tissue with said cryogenicfluid cooling element, and ablating tissue with said RF tissue heatingelement, controlling the steps of cooling tissue with said cryogenicfluid cooling element and ablating tissue with said RF tissue heatingelement with a control console, the control console being operable tocontrol the cooling element and the heating element, measure animpedance input, and adjust tissue heating in response to said impedanceinput.
 7. The method of claim 6, wherein the step of cooling tissue withsaid cryogenic fluid cooling element occurs prior to the step ofablating tissue with said RF tissue heating element.
 8. The method ofclaim 6, wherein the step of cooling tissue with said cryogenic fluidcooling element occurs subsequent to the step of ablating tissue withsaid RF tissue heating element.
 9. The method of claim 6, wherein thestep of cooling tissue with said cryogenic fluid cooling element occurssimultaneously with the step of ablating tissue with said RF tissueheating element.